Since the advent of two-way radio communication, designers have been faced with the challenge of making radio equipment smaller and smaller. The ultimate goal has been to reduce equipment size to the point where it is easy for an individual user to carry and operate it. Any unit intended to be carried by an individual is usually designated as portable, and communication units designed for extremely small size and ease of use are often termed "personal" communication units.
Of course, units designed for the individual user are generally equipped with batteries, since it is assumed that it would be inconvenient to require the user to search for a power source before commencing communication. Indeed, it is the "ready-to-use" nature of portable equipment that constitutes perhaps its greatest appeal.
Naturally, an associated integral battery may add undesired size and weight to portable equipment. But, since battery size and battery capacity are generally directly proportional to one another, frequent users are more tolerant of increased battery size and weight because these users need more "talk time" and "standby time" than infrequent users. The term "talk time," when applied to portable communication units, generally refers to battery life measured while the transmitter portion of the communication unit is active. "Standby time" refers to battery life measured while the communication unit is in a powered-on state, but with the transmitter inactive.
Still, the majority of portable equipment users, and not a small number of frequent users, stress the small size and weight aspects of portable equipment when making a purchase decision. Thus, considerable pressure still exists on designers to make even highcapacity battery assemblies as compact as possible.
Most battery assemblies intended for portable use are designed to be rechargeable to maximize user convenience. It is much more economical to place a battery assembly (or battery pack, as it is sometimes called) into a charger for a period of time than to be compelled to purchase new batteries every time battery voltage drops below a useful level. Extant rechargeable battery packs generally include four contacts disposed on a convenient exterior surface for compatibility with a battery charger. These contacts permit electrical access to components that help to determine, among other things, the desired charge rate for a given battery pack and when the battery is adequately charged. This contact arrangement is an important factor in determining how small a battery pack can be, since exterior surface area must be maintained to accommodate the external contact array.
Accordingly, a need arises for a method for effectively reducing the number of contacts required so that a corresponding reduction may be effected in battery size, weight, cost, and complexity. Of course, this contact reduction must not affect the ability to measure critical battery charging parameters.